Method of making patterns and use thereof



y 20, 1947- E. H. ZAHN :rm. 2,420,851

OF MAKING PATTERNS AND USE THEREOF Filed Julw B. 1943 Patented May 20,1947 lKETHOD OF MAKING PATTERNS AND USE THEREOF Eric H. Zahn,

Feagin, New York, N.

Laboratories, Inc., New York, N.

tion of New York Pound Ridge, and My Chester Y., asslgnors to AustcnalY., a corpora- Application July 8, 1943, Serial No. 493,828

Claims. 1

Our present invention relates generally to the casting art, and hasparticular reference to certain improved procedures to be employed inthe production of cast articles having hollow interiors.

While our invention is not necessarily restricted to the casting of anyparticular type of hollow article. nor to the material of which suchcasting is to be made. it is primarily useful in the production of castmetallic articles of relatively intricate configuration in which thehollow interior is of irregular shape. especially articles of relativelysmall size and accurate dimensions. The mechanical arts abound withillustrations of these types of articles. but for the purposes of thepresent disclosure we have chosen to allude to surgical appliancesintended for permanent implantation in the body to reinforce or replaceportions of the skeleton structure. As a specific example we havedepicted in the accompanying drawings an artificial member designed forsurgical attachment to the upper end of the shaft of the human femur orhip-bone to serve as a permanent replacement for the head portion of thebone. Despite the fact that such an article has unique curvatures andcertain relatively critical dimensions, and the interior of the articleis quite irregular in shape and has numerous "under-cut" portions, thepresent invention permits items of this irregular character to beproduced in finished form. in commercial quantities. by the employmentof pure casting procedures. Usually the casting is made of anon-corrodible heat-resistant alloy, such as chromium-cobalt-molybdenumalloy. and is carried out at high temperatures in molds of suitablerefractory character.

The ultimate casting need not necessarily be made in a one-piece mold.but the advantages of the present invention and its potential usefulnessfor a variety of purposes will be best appreciated by describing itsapplicability to the creation of such molds.

In the formation of a refractory mold of onepiece chari-cter. it isconventional practice to make a pattern of destructible material(such'as wax, for example) which is a replica of the de sired article.This pattern is invested in the mold material and then destroyed (forexample, by melting the wax). thereby leaving a corresponding moldcavity in which the ultimate article may be cast. It is among theobjects of the present invention to provide an improved method of makinga self-sustaining casting pattern composed entirely of destructiblepattern material which is a replica of an article having an irregularlyM 2 shaped hollow interior. More particularly, the present method is onewhich permits such dcstructible patterns to be manufactured incommercial quantities by means of casting operations.

By the term "destructible material," as used herein and in the appendedclaims, we intend to refer generally to the types of materials which arecustomarily employed for making patterns which are to be invested inmold material and then :iestroyed. Theoretically. there is no knownmaterial which is not destructible." but the present use of this term isintended to signify a susceptibility to destruction by relatively simplecommercial procedures such as a heat-treatment which either melts thematerial or burns or volatilizes or otherwise breaks it down. or atreatment with a liquid which has a dissolving or equivalent chemicaleffect upon the material. Various substances which have this type of"desructibility will be illustratlvely specified hereinafter.

Another object of our invention is to provide an improved method ofutilizing a model of the ultimate desired article for the generalpurpose of making a cored mold, and for the specific purpose of making acored mold of sectional character in which destructible patterns of thetype hercinbeiore referred to may be made.

In accordance with our invention, we first form a core of destructiblematerial conforming in shape and size to the hollow interior of thedesired article, and then form the desired pattern around this core, thepattern being composed entirely of differentially destructible material.We then destroy the core to eliminate it from the pattern. By the term"differentially destructible" we allude to the employment of twodifferent materials each of which is destructible by some type ofdestructive action to which the other is immune. Thus, example. by thedestructive action of a solvent in which the pattern material isinsoluble. A convenient and preferred procedure involves the formationof the core and the surrounding pattern of waxes or equivalent materialsof meltable character, the melting temperature of the core beingsuiiiciently below the melting temperature of the pattern so that thecore elimination may be enected by subjecting it to the lowertemperature.

We achieve these general objects and advantages in the mannerillustratively exemplified in the accompanying drawings in which:

Figure 1 is a perspective view of a core whose formation is one of thefirst steps involved in carrying out the present process:

Figure 2 is a diagrammatic cross-sectional view the core elimination maybe eifected. for

through a sectional casting mold in which the core of Figure l isemployed;

Figure 3 is a cross-sectional view taken substantially along the line3-4 of Figure 2;

Figure 4 is a cross-sectional view of the intermediate product resultingfrom the employment of themold ofFigures2and3;

Figure 5 is a cross-sectional view of the destructible pattern which isproduced by eliminating the core from the assembly of Figure 4;

Figure 6 is a diagrammatic cross-sectional view through a one-piecerefractory mold in which the pattern of Figure 5 has been invested andfrom which it has thereupon been eliminated; and

Figure 7 is a perspective view of the ultimate article which is cast inthe mold of Figure 6.

The article I 0 which we have chosen to illustrate (Figure 7) is ahollow artificial femur head, but it will be understood that this itemis merely an illustrative example of a wide variety of differentarticles which may be produced by the practice of the present invention.It should also be mentioned that the article II as illustrated herein isnot intended to be an absolutely accurate representation 01 the surgicalappliance, numerous contour and other details having been omitted forthe sake of simplicity.

The article III has a substantially cylindrical stem portion Ii mergingwith an oblique neck I 2 upon which a substantially spherical head II isformed. The stem II is ultimately intended to be secured by any suitabletechnique of bone surgery to the shaft portion of the femur which is tobe re-built, while the rounded head it is intended to establish apivotal relationship within the corresponding socket of the aoetabulum.At the Junction of the neck I: with the stem p rtion ii there areirregular protuberances (indicated generally by the reference numeral M)which correspond to the eminences normally present on a natural femur(known as trochanters) for muscle-attachment purposes. In the artificialdevice, these protuberances ll may be provided with loops or the like tofacilitate suturing.

For the sake of lightness in weight, the artificial appliance is madesubstantially hollow as indicated in Figure '7. being in eilect a mereshell of suitable material (such as an alloy of the characterhereinbefore mentioned) whose strength. stability, chemical resistanceand other properties are adequate for the purpose. The opening in theend of the head It, formed there by virtue of the correspondingeLLension ll (see Figure 1), is sealed up by means of a plug or the likewhich may be welded into position during the final manui'acturingstages.

In carrying out our invention, we first form a core I! (Figure 1) whichconforms in shape and size to the interior cavity within the item II.This core is composed of destructible material, and it is provided withextensions I I at its opposite ends to permit it to be properlypositioned within a sectional mold such as that shown in Figures 2 and3. v

This mold is composed of two or more separable complementary sections(such as the four sections l1 herein illustrated by way of example),these sections being provided with special openings which accommodatethe extensions I l, as shown, and provided with a casting cavity I.which conforms in shape and size to the external characteristics of thedesired article. The mold is composed of some suitable permanentmaterial, such as metal. and may be of any conventional structuralcharacter provided with positioning lugs 4 and the like (not shown) tofacilitate the assembly and disassembly of the mold sections. A sprue orsprues are formed in a suitable locality to permit the introduction ofthe material which is to be cast around the core l5.

Into this mold we introduce a material which is of differentialdestructibility with respect to the core i5, and the ultimate result isa castin as shown in Figure 4 in which the core 1.5 is embedded. Thecast body It is a replica of the item I0, and by now destroying the coreI! to eliminate it from the surrounding material a body of the charactershown in Figure 5 is produced. This body is identical in shape. size.and contour details with the item I 0, except that it is composedentirely oi destructible pattern material.

This destructible pattern is then invested in mold material 20 (seeFigure 6) which may be, for example, of refractory composition. Afterthe mold material has set, the pattern i5 is destroyed and eliminated,thereby leaving a casting cavity ii of corresponding contour and shape.In accomplishing this result, the pattern It is preliminarily associatedwith a suitable projecting portion or portions of like destructiblematerial so as to form the sprue opening I! in the mold 20. It isthrough this opening, and such other openings as may be provided for thesame purpose. that the material of the pattern It, when destroyed, isallowed to escape. For example, if the pattern is of meltable material,its elimination from the mold 20 would be accomplished by subjecting itto heat and allowing the molten pattern material to flow out through theopening 22.

The opening 22 serves also as a passage-way for the introduction of theultimate metallic material of which the final casting is to be made. Ifthe casting is to be composed of a chromiumcobalt-molybdenum alloy, forexample, the mold 20 is usually predicated to a temperature of about2000 F., and the molten alloy is usually heated to a temperature ofabout 2800' F., and is introduced into the mold 20 under pressure.Ultimately, the mold II is destroyed to free the casting which has beenformed within it.

In forming the cored mold of Figures 2 and 3, we prefer to employ thefollowing procedure. A solid model is first made either of wood, ivory,metal, or any other desired composition. which conforms in externalshape and size to the ex-- ternal characteristics of the desiredarticle. This model has the external appearance, when first formed, ofthe structure shown in Figure 4 of the present drawings. It is employedin any conventional or suitable manner to form the complementary moldsections i1 and in achieving this result it may be desirable, forexample, to employ the procedure described and illustrated in Patent No.2,308,516. The model is then altered, by carving or whittling it down,or otherwise reducing and changing its shape and possibly addinglocating tabs or the like, so that it ultimately appears like the itemshown in Figure 1 of the present drawings. Its body portion now conformsin shape and size to the hollow interior of the desired article. Thisaltered model is then utilized in any suitable or desired manner to formanother set of separable complementary mold sections (not shown) whichare also composed of metal or equivalent permanent material. and informing these mold section. the procedure illustrated and described inPatent No. 2,806,516 may be employed. if desired. The

model has then iuliilled its functions and m y bedlsposed of.

We then have available two sectional casting molds of permanentcharacter which may be used repeatedly. One of them permits theproduction oi cores as shown in Figure 1. The other is illustrated inFigures 2 and 3 and is used repeatcdly in the manner herein described toproduce pattern-core assemblies as shown in Fisure 4. Obviously, ifdesired. the mold which forms the core I! may be constructed with amultiplicity of casting cavities so that a plurailty'oi cores may beproduced at the same time. The mold of Figures 2 and 3 may also beconstructed, if desired, with a series or separate casting cavities,preferably communicating with one another, so that a plurality ofdestructible patterns may be formed in one operation.

The materials of which the core and pattern are made may be of varioustypes. For example, they may be so chosen as to have difierentlalcharacteristics of solubility. Thus, the core might be of water-soluble(or water-dispersable) material while the pattern material is insolublein water. Among the water-soluble or -dispersabls materials of which thecore could be composed are certain oi the polyhydric alcohol esters suchas di-glycol stearate, di-ethylene-glycol monostearate, glyceryltartrate, or the like; or certain dehydrated condensed glycols such asthe polyglycols; or certain of the polyallrylene oxides (currentlyavailable under the name "carbowax"): or acetamide. To any selected oneor more oi these materials polyvinyl alcohol might well be added toimpart greater strength.

Among other materials of water-soluble character which might be employedto form the core are numerous salts which are very soluble in hotsolutions and less soluble in cold solutions, and which are adapted totake up water or crystallisation. For example, salts such as sodiumthiosulphate; magnesium chloride, sodium bichromate, and ammoniumaluminum sulphate are oi this type and have been found satisfactory informing strong cores with smooth surfaces. The cores may be i'ormed bycrystallization from hot supersaturated solutions of the salts, e. g.,by introducing such hot solutions into the core molds and allowing thecrystalline hydrate to term as cooling proceeds. Calcium chloride istypical oi another kind of salt which could be used in much the samemanner, except that calcium chloride takes up alcohol of crystallizationto form a crystalline water-soluble cor material. Accordingly, the useof salts ior the present purpose is not necessarily restricted to watersolutions but may involve alcohol solutions as well, or water-alcoholsolutions.

with a core 0! this type. susceptible to destruc tion and elimination bysubjection to an aqueous treatment, any of a large group of materials,insoluble in or immune to water, might be emlayed for the outer pattern.For example, any or the commonly-employed wax mixtures could be used.such as a mixture of carnauba, candelila, and beeswax, with or withoutperaflin: or a mixture or the foregoing with polymeriaed terpene: or amixture or oarnauba, paraiiin. and polybutene. Other possible materialsare acrylic resin, or polystyrene resin, or mixtures at these substanceswith other resins, waxes, or the like. In 'each case. the patternmaterial is or moldable (i. a, eastable) character, and is destruotibleto permit its ultimate elimination from the one- 6 piece mold in whichit is to be invested. For example, it wax mixtures are employed, theycan be eliminated by the dissolving action 01' a suitable solvent, or bymelting them or by other means; and ii acrylic or polystyrene resins orthe like are employed, they can be eliminated by the destructive burningor decomposing action oi heat, or by other means.

Most of the foregoing illustratlvely specified pattern materials are notsoluble in ethyl alcohol, hence an alternative way oi carrying out theprocess may reside in using any 0! these materials to form a patternwhich is cast around a core composed of a material which will yield tothe dissolving action oi ethyl alcohol. Among such alcohol-solublematerials, suitable for the present purpose, might be mentioned sorbitollactate, sorbitol dl-stearabc, polyvinyl acetate resin, acetamide, orthe like.

Another way of providing for the desired diiierential destructibility oithe core and pattern materials is to compose the core of a relativelylowmelting-point substance. For example. it the outer pattern is formedof one or the conventionally-employed wax mixtures it may have a meltingpoint 01' approximately 76 C. In the case of carnauba wax mixtures themelting point might be approximately 83'-86 C. The core might then becomposed, for example, oi any of the following illustrative materials:

Yellow beeswax, which melts at 61' (3.,

Cocoa butter, which melts at 3045 C.,

Di-glycol stearate, which melts at 53 C.,

Levulinic acid, which melts at 33' C.,

Bomyl acetate, which melts at 29' C.,

Tetrachloro (l, 2, 3, 4) benzene, which melts at or of any othersuitable material having a melting temperature appreciably lower thanthat oi the pattern material, care being taken, of course. when thepattern material is formed around the core, that the latter isadequately pre-chilled or otherwise guarded against destruction at thisstage or the process. Ultimately, the destruction of the core and itsconsequent elimination from the pattern may then be accomplished bymerely subjecting it under controlled conditions (e. g., in a water bathor the like) to the lower temperature.

In each case, a number of types of powdered or ground tillers may beused in either the core matcrial or the pattern material or both. Suchfillers might consist, for example, of acrylic or vinyl resins, orsimple inorganic or organic compounds and waxes, and it properly chosenthey serve to decrease shrinkage of the core or pattern, a the case maybe, and help to produce more accurate results.

It will be understood, of course, that the invention is not restrictedto the use of the particular materials mentioned merely by way ofexample, ".0? to the particular modes of core or pattern destructiondescribed. The core may be destroyed and thus eliminated from thepattern by any suitable or desired procedure so long as it leaves thedestructlble pattern it let for its contemplated subsequent investment:and the destruction of the pattern to eliminate it from the moldmaterial in which it is invested may similerly be accomplished by anysuitable or desired means. The important i'eature oi the inventionresides in the proper selection of the destructible materials employedto form the core and pattern, wherebythestepsottheentireprocessmaybe2,42o,ss1

7 satisfactorily carried out, as described, in a wholly feasible andcommercially utillzable manner.

In general it will be understood that the details herein described andillustrated are intended to be merely illustrative in character, andthat the present process may be applied to a large variety of differentpurposes, and may readily be modified in numerous ways by those skilledin the art without departure from the spirit and scope of the inventionas expressed in the appended claims,

Having thus described our invention and illustrated its use, what weclaim as new and desire to secure by Letters Patent is:

1. A method of making a cast metallic article having a hollow interior,which consists in forming a core of destructible material conforming tosaid hollow interior, casting differentially destructible materialaround said core to form a destructible pattern which is a replica ofthe desired article, destroying the core to eliminate it from saidpattern, said core elimination bein effected by subjecting it to adestructive action to which the pattern material is immune, investingthe resultant hollow pattern in refractory mold material and thendestroying it to eliminate it and thereby leave a corresponding moldcavity in the refractory material, and casting the desired metallicarticle in said cavity.

2. A method of making a cast metallic article having a hollow interior,which consists in forming a core of destructlble material conforming tosaid hollow interior, casting differentially destructible wax materialaround said core to form a destructible wax pattern which is a replicaof the desired article, destroying the core to eliminate it from saidpattern, said core elimination being affected by subjecting it to adestructive action to which the wax pattern material is immune,investing the resultant hollow wax pattern in refractory mold materialand then destroying it to eliminate it and thereby leave a correspondingmold cavity in the refractory material, and casting the desired metallicarticle in said cavity.

3. A method of making a cast metallic article having a hollow interior,which consists in forming a core of destructible material conforming tosaid hollow interior, casting differentially destructible materialaround said core to form a destructible pattern which is a replica ofthe desired article, destroying the core to eliminate it from saidpattern, said core elimination being effected by subjecting it to thedestructive action of a solvent in which the pattern material isinsoluble, investing the resulting hollow pattern in refractory moldmaterial and then destroying it 8 to eliminate it and thereby leave acorresponding mold cavity in the refractory material, and casting thedesired metallic article in said cavity.

4. A method of making a cast metallic article having a hollow interior,which consists in forming a core of destructlble material conforming tosaid hollow interior, casting differentially destruetible materialaround said core to form a destructible pattern which is a replica ofthe desired article, destroying the core to eliminate it from saidpattern, said core elimination being effected by subjecting it to adestructive heat treatment to which the pattern material is immune,investing the resultant hollow pattern in refractory mold material andthen destroying it to eliminate it and thereby leave a correspondingmold cavity in the refractory material, and casting the desired metallicarticle in said cavity.

5. A method of making a cast metallic article having a hollow interior,which consists in forming a core of destructible material conforming tosaid hollow interior, casting differentially destructible materialaround said core to form a destruotible pattern which is a replica ofthe desired article. destroying the core to eliminate it from saidpattern, said core being composed of a material which melts at atemperature below the melting temperature of the pattern material, andsaid core elimination being effected by melting it at said lowertemperature, investing the resultant hollow pattern in refractory moldmaterial and then destroying it to eliminate it and thereby-leave acorresponding mold cavity in the refractory material, and casting thedesired metallic article in said cavity.

- ERIC H. ZAHN.

ROY CHESTER FEAGIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,017,218 Marcus Oct. 15, 19351,384,123 Lougheed Jan. 4, 1921 1,421,988 Richards July 4, 19221,666,840 Diliman Dec. 22, 1925 1,554,597 Alden Sept. 22, 1925 1,697,438Wagenhorst Jan. 1, 1929 FOREIGN PATENTS Number Country Date 151 GreatBritain 1869

